1. Field of the Invention
The present invention generally relates to folding sheet material and, more particularly, to a sheet folding apparatus using a fold blade that includes a rounded folding surface.
2. Background Information
Several methods for creating folds in sheet material are currently known, including the use of dual folding cylinders, as described in U.S. Pat. No. 4,053,150 (Lane), U.S. Pat. No. 4,893,803 (Peterson), and U.S. Pat. No. 4,643,705 (Bober), the disclosures of which are hereby incorporated by reference in their entireties. Another known method for folding sheet material involves the use of an in-line series of concave V-shaped pulleys, as described in U.S. Pat. No. 6,120,427 (Haan et al.), the disclosure of which is hereby incorporated by reference in its entirety. A method for folding sheet material is also described in PCT Document No. WO 00/18583 (hereafter referred to as “the Trovinger PCT”), hereby incorporated by reference in its entirety, where a fold is formed in a sheet material by reciprocating a set of fold rollers that have been placed into contact with the sheet material against a sharp-edged fold blade.
In each of these methods and associated systems, sheet material is deformed to create sharp, creased folds. However, creating products such as booklets out of sheet material containing such folds can have its disadvantages. For example, in a booklet-making environment, a condition known as “pillowing” can occur even when the booklet contains only a few sheets of material. Pillowing describes the tendency of booklet pages to spring open near the folded edge of a booklet and can be the limiting factor when designing a booklet. That is, a booklet with containing too many sharply folded sheets (depending on the material used) can possess excessive pillowing and can consequently be both difficult to handle and unsightly.
It would be desirable to create a fold that reduces pillowing and is cosmetically more appealing than a sharp fold.